Two warm ocean currents: Gulf Stream, Brazil Current*.

Here are the answers based on the provided text and map:

1. a)

   • Two warm ocean currents: Gulf Stream, Brazil Current.
   • Two cold ocean currents: Labrador Current, Benguela Current.

   b)

   • Gulf Stream: Flows generally northeast.
   • Brazil Current: Flows generally southwest.
   • Labrador Current: Flows generally south.
   • Benguela Current: Flows generally northwest.

2. Ocean currents are warm or cold depending on their origin. Warm ocean currents originate near the equator, where solar radiation is intense, heating the water. They then flow towards the poles. Cold ocean currents originate near the poles, where temperatures are low, cooling the water. They then flow towards the equator.

3. Many of the world's deserts are on the west coast of continents because of the influence of cold ocean currents. When air passes over a cold ocean current, it is cooled significantly. This cold air has a reduced capacity to hold moisture, causing it to become dry. As this dry air moves over the adjacent land on the west coast, it prevents rainfall, leading to arid conditions and the formation of deserts.